Hempcrete is often though of as a carbon “negative” material, or a construction material that stores more carbon than it emits. Yet, how much carbon can it store? Well, that depends on a numerous factors, primarily the type of binder used and the density of the mix.
I’m excited to share the results of our recent project in which we developed a simple model for quantifying the carbon uptake of hempcrete, considering both the carbon stored during photosynthesis (plant growth), and carbon stored via carbonation of the binder (considering both CH and CSH). We applied this model in a life cycle assessment of 36 hempcrete mix designs of various densities and binder compositions to compare cradle-to-gate carbon emissions with the carbon uptake for a 1 square meter wall with a U-value of 0.27 W/m2K). We found that up to 16 kg CO2/m2 of wall could be stored, yet not all mix designs we looked at resulted in net carbon storage. For example high density mixtures (425 kg/m3) using ordinary portland cement as a hydraulic binder (with hydrated lime) emitted 8.16 kg CO2/m2 of wall, even when considering the carbon uptake of carbonation and photosynthesis.
For a look at the results of all 36 mix designs and the model, check out the publication. It is available for free download for the next couple of weeks.